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Anaerobic digestion is a critical technology in the bio-based economy and can be applied to convert a wide range of organic substrates into methane. It can help us to come true the carbon neutrality of wastewater treatment systems. Mono-digestion of kitchen waste often occurred with volatile fatty acids (VFAs) accumulation and ended in process failure. The single digestion of sludge, with a limited biodegradability, results in poor anaerobic digestion performance. Considering that, a series of batch mesophilic co-digestion of kitchen waste (KW) with different ratio of VS/TS (‘f’) of A-sludge were performed to evaluate the effect of ‘f’ on the co-digestion performance. A-sludge is produced during the highly loaded first stage of the two-phase ‘Adsorptions- Belebungsverfahren’ or A/B activated sludge system. We obtained A-sludge with different ‘f’ (0.41, 0.55, 0.71) by controlling the parameters (hydraulic retention time (HRT), organic loading rate (OLR), sludge retention time (SRT), dissolved oxygen (DO)) of A-stage of A/B process. The results revealed that co-digestion of appropriate fraction of kitchen waste with high ‘f’ A-sludge could stimulate VS removal, total methane yield and total volumetric productivity, which increased by 1.40-fold, 2.38- fold, 3.30-fold as the ratio of ‘f’ was increased from 0.41 to 0.71 without KW in the substrate, respectively. 1.36-fold, 2.16-fold and 2.93-fold corresponding to 10%t of KW in the substrate. The most optimum performance can be obtained in the 20% of kitchen waste with an ‘f’ value 0.55 of A-sludge in the substrate. [ABSTRACT FROM AUTHOR]

The performance of simultaneous nitrification and denitrification (SND) via nitrite including partial nitrification and SND was investigated in a pilot-scale-modified anaerobic–anoxic– oxic reactor. Since partial nitrification and SND need a similar requirement on dissolved oxygen (DO) level, a low DO was kept in the operation for achieving SND via nitrite. Results showed that SND via nitrite succeeded between 0.4 and 1.6 mg/L DO concentration. The average total nitrogen (TN) removal efficiency was 67.5%. Four forms of biodenitrification were quantified via the estimation of material balance and calculation of SND. SND via nitrite compared with the other three forms made 32.3% contribution to biodenitrification. The operation of a wastewater treatment plant was continuously studied as a comparison with the pilot reactor. With the same raw water, SND not only saved 82.6% of oxygen consumption as well as 30.4% of carbon source, but also owned a higher effluent quality on TN at 11.2 mg/L. Denaturing gradient gel electrophoresis results showed that after long-term hypoxia acclimation, the dominant denitrifier community changed and the abundance ratio of ammonia-oxidizing bacteria/nitrite-oxidizing bacteria was increased. [ABSTRACT FROM AUTHOR]